Study of the Stress State of a Dissimilar Metal Weld Due to Manufacturing and Operational Conditions

Abstract

Welding is accompanied by the presence of weld residual stresses, which in case of dissimilar metal welds even with post weld heat treatment cannot be removed completely therefore they should be considered when assessing possible welding defects. The measurement of residual stress in metal weld is a very complex procedure and also in the investigated case could not be carried out as it is the part of a working plant. However, by modelling these processes, the residual stresses and deformation of the components caused by this manufacturing method can be determined. It is important to calculate these values as accurately as possible to determine the maximum load capacity of the structure. The structure under examination was the dissimilar metal weld of a VVER-440 steam generator. 2D simulations were performed, where temperature and phase-dependent material properties were implemented. Different loading scenarios were considered in the numerical analysis. The results can be useful to determine the real loading conditions of a given component and can be used to predict stress corrosion crack initiation locations, as well as to evaluate the lifetime and failure mode prediction of welded joints.

Supporting Imaging of Austenitic Welds with Finite Element Welding Simulation—Which Parameters Matter?

“…The chemical compositions of the materials are listed in Table 1. Using these data, the temperature-dependent material properties were derived using the JMatPro software [19][20][21]. These properties include Young's modulus (E), yield strength (σ y ), specific heat capacity (c), thermal expansion coefficient (α), and thermal conductivity (λ).…”

Feasibility of Safe Operation of WWER-440-Type Nuclear Power Plants for Up to 60–70 Years

“…According to [48], the degradation mechanisms for the flaws in the dissimilar material welds at WWERs are usually a combination of corrosion on the carbon steel side and stress-corrosion-cracking interdendritic character. The factors determining the cracking, i.e., the stresses, the material, and the environment have been thoroughly investigated, e.g., [48][49][50][51][52][53][54][55][56][57][58]. Cases of DMW degradations have been found and repaired at Dukovany NPP and Kola NPP [48,57,58].…”

“…Cases of DMW degradations have been found and repaired at Dukovany NPP and Kola NPP [48,57,58]. The approach of ASME, 2013 Section XI was applied to evaluate allowable flaw sizes in the DMW connecting the austenitic stainless-steel primary pipe to the K22 ferritic steel body of the steam generator [52,53]. A thorough nondestructive examination indicates the performance of these newly repaired DMWs [58].…”

“…In the future, efforts should be made to collect, evaluate, and analyze the operators' operational data and in-service inspection results [44]. The WWER-440-related experiences are summarized in several documents and studies, e.g., [48][49][50][51][52][53][54][55]. During the long-term operation of the SG, corrosion damages have been found that were related to intercrystallite corrosion of metal 10Ch16N25АM6, built-up by electrodes EA 395/9 [48].…”